At present, a wide variety of IMDs are commercially released or proposed for clinical implantation in the human body. Certain IMDs are manufactured as discrete units that are intended to be selected by an implanting physician for a particular clinical use to be coupled together at implantation and to function as a unit. Typically, such IMDs comprise an implantable pulse generator (IPG) or a physiologic monitor and at least one elongated electrical medical lead that are electrically and mechanically connected together upon implantation. Such IMDs include for example, implantable cardiac pacemakers for pacing one or more heart chamber, implantable cardioverter/defibrillators (ICDs) providing automatic cardioversion/defibrillation, anti-tachycardia pacing and bradycardia pacing functions of one or more heart chamber, cardiomyostimulators, cochlear implants, muscle and nerve stimulators, e.g., sacral nerve stimulators, spinal nerve stimulators and deep brain stimulators, and cardiac and other physiologic monitors.
The IPGs of cardiac pacemakers, ICDs, and the various tissue, organ and nerve stimulators typically comprise signal processing and/or pulse generating circuitry powered by a battery and enclosed within a hermetically sealed enclosure or housing, sometimes referred to as a “can”, and a connector header attached to the housing that enables attachment of at least one elongated electrical medical lead. Certain implantable hemodynamic monitors also comprise a hermetically sealed housing and connector header that enables attachment of at least one elongated electrical medical lead. Other implantable monitors comprise a hermetically sealed housing and a sensor header that only supports a sensor, e.g., an EGM sense electrode.
The hermetically sealed housings are typically formed of a conductive biocompatible metal, although proposals have been made to form hermetically sealed housings of a non-conductive, biocompatible polymeric or ceramic. The opposed major sides of the IPG or monitor housing can be shaped having substantially circular, oval or rectilinear outlines and can have relatively straight and curved side edge sections. The opposed major sides are typically planar and disposed substantially in parallel, although the major sides may be bowed, convex or concave or otherwise contoured to some degree to conform to a particular implantation site. The opposed major sides are typically supported and joined together at their side edges by a mutual housing sidewall extending between them and having a sidewall width substantially defining the thickness of the hermetically sealed housing. The mutual sidewall extends through a number of sidewall turns or corners depending on the circular, oval or rectilinear outline or combination of such outlines of the opposed major sides. Generally speaking, such IPG and monitor housings are referred to as “prismatic”.
The connector header for making a connection with a proximal connector assembly of an elongated electrical medical lead is physically attached to a header mounting section of the common sidewall that is typically, although no necessarily, planar. The connector header typically comprises a header body that is fabricated of a relatively hard, dielectric, non-conductive polymer encasing and isolating electrically conductive components from the patient's body. The connector header has a header thickness generally corresponding to the housing thickness and a header mounting surface that conforms to and is mechanically affixed against a mating housing sidewall mounting surface. The connector header has a header height measured in a direction extending away from the housing sidewall mounting surface and a header width measured in a direction extending along the housing header mounting surface in the width dimension of the housing. Various examples of connector headers and hermetically sealed housings are found in the patents referenced herein.
It is generally desirable that the connection of an electrical medical lead with an IPG or monitor be made rapidly and in a fail-safe manner during the initial implantation. Moreover, it is desirable to be able to explant the IPG or monitor at a later time in order to disconnect the electrical medical lead and either replace the IPG or monitor or replace the electrical medical lead.
Typical IPG and monitor connector headers are formed having at least one electrically conductive, header connector element or connector block embedded in the insulating material. Each connector block is connected by means of an insulated feed-through mounted to the hermetically sealed housing to the circuitry within the housing. Typical connector blocks are formed having a threaded bore for receiving a setscrew and a connector block bore extending at substantially right angles to the threaded bore for receiving a lead connector element. The connector block bore is axially aligned with a header connector bore extending from the connector block through the header body to an exterior surface thereof. The threaded bore and setscrew are axially aligned with a further header aperture extending from the connector block through the header body to an exterior surface thereof.
At implantation, the proximal connector assembly of the electrical medical lead is inserted into the header connector bore to locate a lead connector element, e.g., a lead connector pin or ring, within a connector block bore. A tightening tool, e.g., a hex wrench, is inserted through the further header aperture to engage a setscrew socket and rotate the setscrew against the lead connector element, thereby clamping the connector element against an inner surface of the connector block and ensuring electrical contact between a lead conductor of the electrical medical lead and the circuitry of the IPG or monitor. The attachment is reliable over long-term chronic implantation if the setscrew is properly tightened.
Over long-term chronic implantation, it is desirable to ensure that body fluids do not pass through the further header aperture and header connector bore to the connection made between the setscrew and the lead connector element within the connector block bore so that the IPG does not fail. Sealing rings are typically formed around the proximal connector assembly of the electrical medical lead that seal against the header connector bore upon insertion of the lead connector assembly into the header connector bore. Sealing or closing the further header aperture from fluid intrusion is a somewhat more difficult problem to solve, and various methods have been developed and implemented over the years.
In one approach, disclosed in U.S. Pat. No. 4,105,037, for example, the further header aperture is filled with a quantity of liquid silicone medical adhesive after the setscrew is tightened against the lead connector element. It is then necessary to wait for the silicone rubber adhesive to solidify before the implantation can be completed. This approach requires considerable care to complete without leaving voids and bubbles in the applied adhesive that body fluids can pass through. The cured silicone rubber adhesive is also difficult to remove after chronic implantation to be able to replace the electrical medical lead or the IPG or monitor.
In a further approach, various removable plugs have been proposed to fill the further header aperture to seal the setscrew and connector block from body fluids after the setscrew is tightened against the lead connector element as disclosed in U.S. Pat. Nos. 3,822,707, 3,908,668, 4,072,154, and 4,180,078, for example. The plug employed in the '154 patent is formed of a resilient silicone rubber or other biocompatible elastomer or elastomeric compound having an annular ring that fits into an annular groove of the further header aperture to retain the plug within the further header aperture. As shown in U.S. Pat. Nos. 4,141,752, 4,262,673 and 4,316,471, the plug is rigid like the header, and a resilient, silicone rubber, sealing O-ring is trapped and compressed between the plug sidewall and the further header aperture as the plug is inserted and tightened.
Fitting very small rigid or flexible plugs into the further header aperture is difficult, and they can be dislodged and lost during the procedure. The setscrew used to connect the electrode to the stimulator is quite small and if a plug is used to seal the setscrew, the plug is also quite small. From time to time, one or the other is lost on or near the operating table. In addition, due to their small size, both are quite difficult to handle directly by hand, which is quite undesirable during surgery. It is also not possible to immediately confirm that a fluid tight seal has been achieved.
In the '752 patent, the electrically conductive, metal setscrew is embedded within and physically attached to the plug so that the setscrew and plug screw are simultaneously rotated into the aligned setscrew connector bore and further header aperture by a tool engaging the plug to rotate it. The exterior surface of the plug is formed with a metal cap having a Phillips type cruciform opening that is engaged by a driver to rotate the integral cap and setscrew to tighten or loosen it. Again, the combined plug and setscrew can be mishandled, and it is also not always possible to confirm that a fluid tight seal has been achieved.
In U.S. Pat. No. 4,461,194, it is proposed to provide a tool for inserting a setscrew and a plug into the aligned threaded bore and further header aperture, respectively. The tool includes an elongated handle having a first wrench at one handle end and a second wrench at the other handle end. A rigid cap and a sealing member made of a soft sealing implantable medical grade elastomeric material are positioned on the first wrench with the rigid cap nearest the handle. A setscrew is positioned on the end of the wrench adjacent the sealing member and is preferably held on the end of the first wrench with a medical grade adhesive. The rigid cap is frictionally held in a predetermined spaced relationship from the setscrew, preferably, by a cylindrical tube frictionally engaging the periphery of the cap and fixedly attached to the handle portion. The rigid cap and the second wrench are designed such that the second wrench is used to drive the cap and compress the sealing member, thus providing a leak-proof seal. Again, there is a chance that the setscrew and plug will not remain on the handle during the procedure.
In a further approach that is in common use at the present time, the setscrew is partly screwed into the setscrew connector bore during manufacture. A pre-formed sealing member or element, typically referred to as a septum or a grommet, fills the header aperture aligned with the setscrew aperture (referred to in this context as a “grommet aperture”) as disclosed, for example, in the above-referenced '668 patent and in U.S. Pat. Nos. 4,010,762, 4,479,489, 4,932,409, 5,207,218, 5,522,861, and 5,989,077. The pre-formed grommet is typically formed of flexible silicone rubber molded into a disc-shape having an inner end wall disposed toward the connector block and an outer end wall exposed to body fluids and tissue during implantation and a sidewall joining the end walls. A slit is typically formed through the grommet extending between the inner and outer end walls so that a hex wrench can be passed from the outer end wall through the pre-formed slit to engage the setscrew socket and rotate the setscrew. The pre-formed slit is expected to reseal and prevent fluid migration therethrough after the setscrew is withdrawn due to the soft pliant nature of the silicone rubber. At a later time, the IPG or monitor can be surgically exposed, and the hex wrench can be inserted through the pre-formed slit in the penetrable grommet to engage and rotate the setscrew away from the lead connector element, thereby releasing the connector element so that the lead connector assembly can be detached and withdrawn from the header connector bore.
Connector headers employing such penetrable grommets were typically fabricated as described in the above-referenced '668 patent to form a non-conductive, header body adhered to the IPG housing and about the electrically conductive components. The feedthrough pin(s) extending from the IPG housing were connected with the connector block(s), and disposable plug(s) or sleeve(s) were fitted into the connector block bore(s) to extend away from the connector block(s), a penetrable grommet(s) was fitted to extend from the setscrew(s), and a mold was fitted about the sub-assembly. The mold was filled with a biocompatible liquid epoxy, and the mold and disposable plug(s) or sleeve(s) were removed when the epoxy hardened to form a non-conductive, header body about the electrically conductive components. In the above-referenced '489 patent, it appears that a header grommet aperture was formed in the connector header body perhaps by use of a disposable plug, and the pre-formed penetrable grommet was adhered within the header grommet aperture employing an adhesive. The use of adhesive to retain the flexible plug is also suggested in the above-referenced '154 patent.
The penetrable grommet disclosed in the above-referenced '668 patent was quite large in diameter and thickness and was retained in place by molding the epoxy header body about the grommet to fit around an outwardly projecting ridge. Good adhesion was achieved between the epoxy header body and the silicone rubber grommet because of the ability to form such a mechanical interlock and because the thermosetting epoxy adhered well with silicone rubber as it solidified. Moreover, epoxy connector bodies remain relatively rigid and dimensionally stable during chronic implantation, so that separation and loss of adhesion does not readily occur. The use of the penetrable grommet simplified manufacturing and solved many of the problems associated with use of separate caps or plugs that the physician had to use to fill the further header aperture as described above, but other problems were observed over time.
The in situ molding process for forming the connector header body does not lend itself to mass production, since it does not involve use of interchangeable parts, and because the steps have to be done carefully and slowly. Bubbles, voids, surface blemishes and other defects can occur requiring rework or scrapping of the product. These drawbacks became more apparent and difficult to resolve as connector headers were reduced in size and incorporated increasing numbers of connector blocks and feedthroughs.
Consequently, a pre-formed, electrically insulating, dielectric, header body was developed as described in commonly assigned U.S. Pat. Nos. 4,142,532, 4,154,248, 4,182,345, and 4,226,244, and in U.S. Pat. No. 4,445,511, having pre-formed cavities, bores, and apertures for accommodating the connector block(s), feedthrough pin(s), pre-formed penetrable grommet(s), fixation mechanisms for attachment to the IPG or monitor housing, and for providing the header connector bore(s). Various attachment techniques for attaching the connector header body to the hermetically sealed housing involving use of mechanical locking components and adhesive backfilling of voids are also disclosed in these patents.
The pre-formed connector body can be formed of polyurethanes, e.g., PELLETHANE® urethane and TECOTHANE® urethane sold by Upjohn, Inc., a polysulfone, e.g., UDEL® polysulfone sold by Union Carbide, Inc., polymethylpentene, e.g., TPX® polymethylpentene sold by Mitsui and Company, polyvinylidene fluoride, e.g., KYNAR® polyvinylidene fluoride sold by the Allied Chemical, and ethylenechlorotrifluoroethylene, e.g., HALAR® ethylenechlorotrifluoroethylene sold by the Allied Chemical Corporation. Currently, pre-formed connector bodies used by the assignee of the present invention are injection molded of TECOTHANE® urethane because of its recognized biocompatibility and availability for use in IMDs.
The use of the pre-formed header body and these assembly techniques simplified assembly, reduced rework, and reduced chronic failure rate. Over time, such IPGs and monitors employing pre-formed header body fabrication techniques have been advantageously increased in capabilities and longevity while being reduced in thickness, height, and width, which define the displaced volume, and in weight. The reduction in the volume of the connector header has been achieved in part by substantially reducing the dimensions of the pre-formed penetrable grommets fitted into correspondingly reduced size header grommet apertures. However, problems have been observed as the size of the pre-formed penetrable grommets and the corresponding header grommet apertures have been reduced.
The passage of the hex wrench through the pre-formed slit is intended to displace, rather than remove the silicone rubber along the slit. However, the possibility of coring the pre-formed penetrable grommet by the hex wrench inserted through the pre-formed slit increases as the diameter of the pre-formed penetrable grommet is decreased. Even the proper insertion of the hex wrench through the pre-formed slit can cause coring of the silicone rubber and deposition of the cored silicone rubber within the setscrew socket. The cored slit cannot properly seal, and the silicone rubber lodged within the setscrew socket can block insertion of the hex wrench into the socket. The penetrable grommet must be designed to yield so as to move the displaced silicone rubber out of the way as the hex wrench is advanced through the slit.
As disclosed in the above-referenced '489 and '928 patents, a yield space between the inner surface of the grommet and the setscrew is provided to accommodate the silicone rubber of the grommet that is displaced inward by the advancing hex wrench. In the '928 patent, a rigid, ring-shaped, stiffener element is also embedded within the pre-formed grommet surrounding the yield space to stiffen the grommet and lessen the possibility of damage to the grommet by insertion of the hex wrench. Whether or not such an approach has merit, fabrication of such a pre-formed grommet with a rigid, ring-shaped, stiffener element may be difficult.
Even the proper insertion of the hex wrench through the pre-formed slit can also cause loss of adhesion of the grommet to the grommet aperture wall surrounding it unless the penetrable grommet is designed to yield and distribute stresses away from the grommet aperture wall as the hex wrench is advanced through the slit.
The mutual area of contact between the sidewalls of each pre-formed penetrable grommet and the header grommet aperture is necessarily reduced in order to reduce the overall volume of the connector header. The silicone rubber of the pre-formed penetrable grommet does not inherently adhere well with the material, particularly, TECOTHANE® urethane, of the pre-formed connector header body. Forming one or more retention ridge in the header grommet aperture sidewall to engage the sidewall of the silicone rubber grommet as shown in the above-referenced '928 patent, for example, is difficult if not impossible due to the injection molding of the pre-formed connector body from TECOTHANE® urethane.
Consequently, the low adhesion and reduced mutual area of contact between the grommet and header grommet aperture sidewalls has necessitated the use of a medical grade adhesive applied to between the grommet and header grommet aperture sidewalls before the pre-formed grommet is inserted into the header grommet aperture. The application of minute amounts of adhesive complicates assembly, and non-destructive testing of the resulting adhesion strength is difficult to accomplish. The applied adhesive can also intrude into the interior yield space and/or the socket of the setscrew. For these reasons, it would be preferable to eliminate use of adhesive to maintain the pre-formed grommet within the header grommet aperture
Other problems have been observed with the use of silicone rubber to form such penetrable grommets and urethanes to form connector header bodies.
The epoxy or urethane connector header body and the silicone rubber grommet are both translucent and substantially colorless or slightly colored such that there is little visible contrast therebetween, rendering it difficult to visually distinguish a penetrable grommet from the surrounding connector header body and to locate the pre-formed slit. Physicians at times inadvertently insert the hex wrench through the pre-formed slit offset from the central axis of the penetrable grommet or at an improper angle and then have to move the hex wrench about or withdraw and reinsert it to properly seat the hex wrench tool end into the setscrew socket to rotate it. This could cause damage to the penetrable grommet compromising the ability of the pre-formed slit to reseal.
Moreover, the silicone rubber material is “sticky” and tends to adhere to itself across the pre-formed slit with aging so that the pre-formed slit tends to heal. After prolonged storage or chronic implantation, it becomes more difficult to insert a hex wrench through the pre-formed slit without coring or dislodging the penetrable grommet from the header grommet aperture. Sometimes, the pre-formed slit will not open at all, and the silicone rubber or the penetrable grommet is “punched out” when the hex wrench is advanced against it and into the underlying setscrew socket. The setscrew socket becomes plugged by the silicone rubber, and the penetrable grommet no longer seals.
It has also been found that connector header bodies formed of TECOTHANE® urethane exhibit cold flow or creep at points or surfaces where pressure is applied chronically. It has been observed that adhesion is lost between the grommet and header grommet aperture sidewalls when the grommet exerts pressure over time against the header grommet aperture sidewall causing expansion of the header grommet aperture diameter.
In addition, the TECOTHANE® urethane connector header body becomes slightly less rigid and dimensionally stable during chronic implantation in body fluids thereby aggravating the cold flow problem and negatively affecting adhesion with the silicone rubber grommet over time that can lead to spontaneous dislodgement of the grommet. Moreover, the weakened adhesion can be overcome if a replacement procedure requiring insertion of the hex wrench through the grommet slit occurs, and the grommet can be dislodged upon withdrawal of the hex wrench. It would be desirable to eliminate or accommodate the cold flow dimensional instability of the connector header body.
Further problems arise as the setscrews and connector blocks are miniaturized. Setscrews are typically formed without a head or “headless” having a uniform outer diameter extending between the socket end and the working or contact end. The setscrew working end is typically closed or solid, and the setscrew socket is a fraction of the length of the setscrew, limiting the depth of the setscrew socket that can be engaged by the hex wrench. As noted above, it can be difficult to locate such a shallow setscrew socket with the hex wrench, and adhesive and/or dislodged silicone rubber can block the shallow setscrew socket.
Size and fit tolerances of the setscrew thread and the threaded bore must be dictated to ensure that the setscrew can be easily rotated and tightened using a specified low torque applied to the setscrew tool or hex wrench. One problem that has occurred due to the tolerances and the involves the inappropriate positioning during manufacture or spontaneous movement of the setscrew within the threaded bore due simply to handling and shipment that cannot be observed when the setscrew is covered by the penetrable grommet. It has been observed that the setscrew can inadvertently migrate and intrude into the connector block bore to block insertion of a lead connector element into the connector block bore. The physician inserting the connector lead element into the connector block bore may incorrectly assume that it is properly inserted and tighten down the setscrew without making contact, resulting in a connection failure that may or may not be detected at the time of implantation.
In addition, the headless setscrew must be longer than the diameter of the connector block bore to prevent it from being unintentionally advanced all the way through the threaded bore and released into the connector bore. Moreover, tubular lead connector elements in current common use have a range of diameters, and the axially aligned connector header bores and connector block bores are provided in a corresponding range of diameters. Consequently, it has been necessary to either use a headless setscrew longer than the largest connector block bore diameter fitted into correspondingly long threaded bore or to provide a range of setscrews having lengths exceeding the connector block bore diameters. It would be desirable to simplify specification and costs of setscrews by employing a common setscrew for all such connector blocks.
Therefore, despite the improvements that have been made in connector headers over the years, problems remain to be solved in the design and fabrication of connector headers of the type employing penetrable grommets disposed in header grommet apertures overlying fasteners, e.g., setscrews, employed to attach lead connector elements with connector blocks of the connector header.